HomeCaliforniaModoc County
Modoc County, California
Shrink-swell clay limits houses without basements on 27% of Modoc County's mapped land, a higher share than 78% of US counties. A shallow water table limits basements on 15%.
The soil survey maps 49% of the county's land area; these shares describe the mapped part. 100% of the county is in drought on the October 13, 2026 Drought Monitor map. FEMA's flood data list no flood losses here since 2016. 59% of homes were built before 1980, against 50% nationally; the median home dates from 1976.
Data as of October 13, 2026 · sources
expansive clay: shrink-swell limits slab homes
high water table: limits basements
in drought, October 13, 2026
of homes built before 1980
Soil under Modoc County
| Expansive clay (limits slab homes) | 27.3% |
| High water table (limits basements) | 14.6% |
| Septic fields very limited | 75.3% |
| Clay swell (LEP, by area) | 4.9% |
| High-swell land (LEP 6%+) | 29.1% |
| Mapped soil | 1,232,582 acres |
| Soil series | Share here | Series nationally: expansive clay |
|---|---|---|
| Deven | 3% | n/a |
| Karcal | 3% | n/a |
| Bieber | 2% | n/a |
| Delma | 2% | n/a |
| Loveness | 2% | n/a |
| Ninekar | 2% | n/a |
How we count · survey areas CA603 (2025-09-03), CA604 (2025-09-03), CA684 (2025-09-05), CA685 (2025-09-05)
What the numbers mean here
Clay swell averages a linear extensibility of 4.9% by land area here, and 29% of the land reaches USDA's high class (6% or more). Clay like that swells when wet and shrinks when dry, under 27% of the mapped land.
Clay shrinks as it dries: 100% of the county is in drought on the latest map, and 27% of Modoc County's mapped land has shrink-swell clay.
Rain over the 12 months to August 2026: 15.81 in, 2.06 in below the 1991-2020 average year of 17.87 in.
USDA rates 75% of the land very limited for septic absorption fields.
Drought
100% of the county is in drought (D1 or worse) on the October 13, 2026 map. Part of the county was in drought in 28 of the last 52 weeks; the most was 100% of its area, in 7 weeks, most recently on the October 13, 2026 map.
| Category, October 13, 2026 | Share of county |
|---|---|
| D0 abnormally dry or worse | 100% |
| D1 moderate drought or worse | 100% |
| D2 severe or worse | 0% |
| D3 extreme or worse | 0% |
| D4 exceptional | 0% |
Flood losses since 2016
FEMA's flood data list no flood losses in Modoc County since 2016.
Rain
| Average year, 1991-2020 | 17.87 in |
| 12 months to August 2026 | 15.81 in (-2.06) |
| 2025 | 20.83 in (+2.96) |
| Wettest year since 1895 | 1998: 30.57 in |
| Driest year since 1895 | 1959: 9.48 in |
| Days with 1 inch or more, normal at CEDARVILLE (28 mi away) | 0.5 |
Homes
| Housing units | 4,764 |
| Median year built | 1976 |
| Built before 1980 | 59% |
| Built 2000 or later | 13% |
| Owner-occupied | 77% |
| Median value, owner-occupied | $224,700 |
| Single-family detached | 82% |
What repairs cost
Published ranges from cost guides, not quotes. More sources, and where they disagree.
Nearby counties
| Place | Distance | Expansive clay | High water table |
|---|---|---|---|
| Lassen County, CA | 61 mi | 21% | 6% |
| Washoe County, NV | 81 mi | 34% | 3% |
| Lake County, OR | 84 mi | 28% | 11% |
| Klamath County, OR | 89 mi | 20% | 21% |
| Shasta County, CA | 90 mi | 9% | 4% |
| Siskiyou County, CA | 94 mi | 11% | 11% |
| Plumas County, CA | 111 mi | 4% | 2% |
| Jackson County, OR | 115 mi | 31% | 19% |
Sources: USDA SSURGO (September 5, 2025) · US Drought Monitor (October 13, 2026) · FEMA NFIP v3 (September 9, 2026) · NOAA (August 2026) · Census ACS 2020-2024. Methods · Data status